1. Field of the Invention
The present application relates generally to cooling methods and systems, and more particularly, but not by way of limitation, to cooling methods and systems utilizing waste heat to power a cooling process. In another aspect, the present application relates generally to maximizing the thermal properties of a thermoelectric cooler, and more particularly, but not by way of limitation, to methods and systems related to a thermally isolated thermoelectric cooler wherein waste heat is utilized.
2. History of the Related Art
Refrigeration is a process of removing heat from either a substance or an enclosed space. The laws of thermodynamics dictate that heat may only be added or removed from a space through application of energy. Application of energy to facilitate removal of heat from a space is known as a refrigeration cycle. Refrigeration cycles typically differ on the nature of energy that is applied. For example, one such refrigeration cycle is a vapor-compression cycle. The vapor-compression cycle is found in most household refrigerators as well as in many large commercial and industrial refrigeration systems. The vapor-compression cycle utilizes mechanical work, in the form of a compressor, to transfer heat to a refrigerant. The heat is then discharged from the refrigerant to a heat sink.
Another refrigeration cycle is known as absorption refrigeration. In absorption refrigeration, a heat source such as, for example, a kerosene-fueled flame or induction type heater is used to provide energy to power a cooling system. Thermal energy is, therefore, applied in absorption refrigeration. Absorption refrigeration is based on the Thermodynamic principle of latent heat of vaporization. That is, evaporation carries heat, in the form of faster-moving molecules, from one material to another material that preferentially “absorbs” the faster-moving molecules. A well-known example of absorption refrigeration is human sweating. The water in sweat evaporates and is absorbed into the air thus carrying heat away from the body. Absorption refrigeration is a popular alternative to vapor-compression refrigeration, particularly in environments where electricity is unreliable, unavailable, or costly.
A third type of refrigeration is known as thermoelectric cooling. In thermoelectric cooling, a thermoelectric element is used. The thermoelectric element provides cooling through the Peltier Effect. Upon application of a voltage, the thermoelectric element creates a heat flux between a junction of two different types of materials thereby transferring heat from one side of the thermoelectric element to the other. Electrical energy is, therefore, applied in thermoelectric cooling.
In most applications, the thermoelectric element is employed such that a cooler side of the thermoelectric element is thermally exposed to an area to be cooled and a warmer side of the thermoelectric element is exposed to a thermal reservoir or a heat sink. Thus, in conventional use, a thermoelectric element is typically disposed in an open thermal system. That is, heat discharged from the warmer side of the thermoelectric element is typically exhausted to the atmosphere and lost. It would be advantageous if heat discharged from the warmer side of the thermoelectric element could be utilized, thereby allowing the thermoelectric element to be utilized in a closed thermal system.
For example, U.S. Pat. No. 6,295,819, assigned to Midwest Research Institute, discloses a heat pump fluid circuit using a thermoelectric cooler. In this device, fluid is routed across both a hot side and a cold side of a thermoelectric cooler; however, the specification discloses that this is done for the purpose of alternatively delivering heat and cold. That is, the system does not make simultaneous use of the hot side and the cold side of the thermoelectric cooler, thus requiring an exhaust of waste heat via a fan.
Regardless of the refrigeration cycle employed, the laws of thermodynamics dictate that energy can neither be created nor destroyed during operation of any refrigeration cycle. Heat removed from a space to be cooled must be eventually transferred to a heat sink. This is typically termed waste heat. In addition, waste heat is a common byproduct of many mechanical processes such as, for example, operation of an internal combustion engine. In most applications, waste heat is simply lost; however, waste heat has potential to be captured and utilized for other applications.